1. Field of the Invention
This invention relates generally to apparatus and methods for removing and replacing a flexible line within a sheave system, and more particularly, but not by way of limitation, to apparatus and methods for removing and replacing a heavy steel drilling cable within a derrick structure of a drilling rig.
2. Description of the Prior Art (Prior Art Statement)
The following statement is intended to be a prior art statement in compliance with the guidance and requirements of 37 CFR SS1.56, 1.97 and 1.98 and with S609 of the Manual of Patent Examining Procedure.
Although the prior art shows several devices for stringing-up power lines upon telephone poles and the like, very little has been done in the way of automating the stringing-up and removal of drilling cables from oil derrick structures. One very early, somewhat related, device is that of Robison shown in U.S. Pat. No. 1,348,448. Robison merely shows those components of an oil drilling rig which are associated with the drilling cable. No apparatus is shown for use with those components to assist in the stringing-up and removal of the drilling cable from the drilling rig. The components of a typical drilling rig similar to those shown in Robison are described in detail with reference to the present invention in this specification under the sub-title "The Drilling Derrick". Also, a portable type drilling rig of more modern construction is shown in U.S. Pat. No. 3,033,528 to Wilson.
U.S. Pat. No. 3,625,445 to Hall shows a device somewhat similar to the friction drive collars of the present invention.
The following U.S. Patents are of interest in that they show various prior art devices for the stringing of transmission wires upon telephone poles and the like. It will be apparent, however, that their relevance to the present invention is slight in that none of them show an apparatus which could be used for the stringing-up and taking down of drilling cables from an oil derrick. These U.S. patents are No. 3,520,489 to Flowers; No. 3,091,413 to Leithiser; and No. 3,073,574 to Garnett.
Also of interest are the prior art methods which have been used for removing and replacing drilling cables within a drilling rig. These prior art methods have been rather unsophisticated brute force methods involving mainly the manual placement of the lines within a sheave system and involving methods of removal which again require a great deal of manual labor. These prior art methods are described in detail in this specification under the sub-title "Standard Rig Methods". It is apparent from those methods there described, which methods are currently in use throughout the drilling industry, that the prior art is void of any apparatus or methods having any substantial similarity to those of the present invention.